Electron discharge device and circuits for neutralized coaxial line amplifiers



June 23, 1953 E. M. BRADBURD 2,643,302 ELECTRON DISCHARGE DEVICE AND CIRCUITS FOR NEUTRALIZED COAXIAL LINE AMPLIFIERS Filed March 51, 1950 akyi i 32 I 44 a/ 29 2a 7 fi INVENTOR ERV/N l4- BRADBURD ATTORNEY Patented June 23, g 1953 ELECTRON DISCHARGE DEVICE AND CIR- CUITS FOR NEUTRALIZED COAXIAL LINE AMPLIFIERS Ervin M. Bradburd, Fairlawn, N. J assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application March 31, 1950, Serial No. 153,136

2 Claims. 1

This invention relates to electron discharge devices and circuits particularly designed for neutralized coaxial line amplifiers.

In the use of amplifiers for very high frequencies and ultra-high frequencies particularly it is desired to use tubes which may be incorporated directly in coaxial lines to serve as amplifiers. To avoid instability of operation it is desirable that the amplifiers have incorporated circuits for neutralizing certain of the inherent tube capacities. Such neutralizing circuits have in the past presented quite a difficult design problem. The conventional electron tubes have a cathode lead at one end, only, and it has been necessary in many cases to provide complex grid and anode connections referred to as grid bells to secure the desired coupling for introducing a neutralizing inductance, or a feedback control in an oscillator.

It is an object of my invention to provide electron discharge devices designed for simple neutralizing connection in a coaxial line amplifier, or providing for proper feedback in an oscillator and to provide simple neutralizing or feedback circuits for amplifiers incorporating such electron discharge devices.

In accordance with a feature of my invention I provide in an electron discharge device having external connections for coupling coaxial line elements to anode and grid electrodes, and a concentrically mounted cathode, a lead connection to the cathode extending out of the opposite end of the envelope connecting to the normal cathode load. Coaxial line coupling can thus be readily made at both ends of the tube to the cathode.

In the normally so called grounded anode tube circuit having a cathode impedance output the neutralizing inductance or feedback control'for the cathode-grid capacitance can be readily obtained between the cathode extension and the external grid connections without disturbing the anode-cathode output resonator.

In the so called grounded grid amplifier, the anode-cathode capacitance may be neutralized by a simple coupling between the extended cathode lead' and anode external connections without disturbing or modifying the direct gridcathode input circuit.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with'the accompanying drawinga-in which:

Fig. l is a diagram, partly in section, of an example of my invention, incorporated in a grounded anode amplifier or oscillator circuit.

Fig. 2 is the equivalent diagram of Fig. 1;

Fig. 3 is a diagram, partly in section, of an example of my invention applied to a grounded grid amplifier and Fig. 4 is an equivalent circuit diagram of Fig. 3.

Turning first to Figs. 1 and 2, there is shown a vacuum tube I having an anode 2, a grid 3, and a cathode 4. The anode 2 may be in an annular form having a portion extending outside the envelope. Grid 3 may be supported on a grid cone 5 extending outside the envelope and provided with a further cylindrical extension 6. Cathode 4 may be supported on a conical extension 1 extending through the envelope which may be connected to a further cylindrical extension or cathode lead 8. On cathode 4 is connected a second cathode lead 9 extending outside of the envelope of tube l in the opposite direction from the lead 8. The cathode i may be heated by any type of the heater arrangement coupled to a heat source by means of leads [0.

It will be immediately apparent that this vacuum tube differs from the conventional type in that a second cathode extension lead 9 is provided. As shown in Fig. l the vacuum tube is incorporated in a coaxial line type of amplifier comprising an outer cylindrical conductor shell II to which the anode 2 of tube 1 is capacitively coupled and which may be considered as being at ground potential. The capacitance between anode 2 and the outer surface of shell ii is sufficiently great that at the operating frequency the anode may be considered substantially to be at ground potential. Mounted within shell H is a further cylindrical conductor H! which extends over the end of conductor 6 so as to provide substantial capacitance which is effectively short circuit for alternating current energy. However this capacitance serves as a D. C. blocking condenser keeping the ground potential on grid I. An annular shiftable plunger l3 may be arranged between conductor i2 and the inner surface of shell ii to provide a tuning resonator for the amplifier input. The resonator formed thereby is designated in Fig. 2 as the grid impedance Zg. The input energy may be supplied to the amplifier by means of a co axial line having its outer conductor i 2- connected to shell II and its inner conductor it connected to conductor [2.

The output energy is taken across a cathode impedance which comprises a resonator cavity formed by the inner surface of shell II and the outer surface of the cathode lead 8. The impedance of this circuit may be adjusted by means of the annular adjustable tuning plunger IS. The impedance of this resonator is shown in the equivalent diagram (Fig. 2) as Zr. The output lead may consist of a second coaxial line having an outer conductor 11 connected to the outer shell H and an inner conductor [8 connected to lead 8.

In operation potentials for the tube may be supplied from a source, shown as battery] 9, having its positive terminal coupledby way of a radio frequency choke and coaxial line 21 to anode 2. An intermediate pointof battery l9 and the outer surface of shell H are grounded as shown at 22. Negative biasing potential may-be applied from battery l9 by means of the coaxial line 23, the inner conductor of which is coupled to the cylindrical extension 6 of the grid.

It will be seen that this structure as so far defined provides a so called grounded anode amplifier .of the coaxial line type in which the output is taken across the cathode impedance. In order that the capacitance betweenthe grid and cathode may be controlled in value or completely neutralised an annular tuning plunger 24 is provided interconnecting the inner surface of conductor [2 and the second or auxiliary lead 9 of cathode 4. This tuning plunger may be adjusted to such a position that the resonator formed within conductor 12 and extension 6 presents the desired inductance LN (Fig. 2) to comensate for the inherent cathode-grid capacitance Cgk (Fig. 2). If it is desired to let the tube circuit oscillate, the feedback neutralization may be made less than complete. Thus the normal high capacitance may be controlledto the desired degree.

It will be'apparent from the foregoing description that by providing a tube having the'additional extension on the cathode control orneutralising compensation may be very simply effected in the coaxial line amplifier. In the con- .ventional type of amplifier wherein the. cathode has lead lines from only one end of the tube a much more complex system is required to effect the compensation.

Turning now to Figs. 3 and 4 I have shown principles of'my invention applied to a coaxial line vacuum tube amplifierof thegrounded grid type. This arrangement comprises a vacuum tube 25 having an anode 26, a grid-2T and a cathode 28. Here again, the cathode is provided'with a conventional input lead comprising a conical element 29 with a cylindrical extension 30 serving as a cathode lead. Heating conductor 31 may be provided for supplying the heat to the indirectly heated cathode. An extension 32 is provided which extends from the cathode 28 at the opposite end of the tube from lead. Grid 21 is provided with an annular flange 33 extending outside the envelope, which flange may be provided with an extended portion 34 to provide better capacitive coupling with the external circuit. I

The amplifier circuit may comprise an outer coaxial conductor shell 35 which may be grounded. Shell 35 and the portion 34 of flange 33 are closely spaced to provide substantial grounding of the alternating current energy while providing a D. C. blocking for the grid bias supply. The grid bias potential maybe applied to the grid byway ofa coaxial line 36.

The anode supply potential may be applied thereto by means of a coaxial line 31 as shown. Input energy may be supplied to the amplifier by way of the coaxial line composed of a portion of outer conductor 35-and conductor lead 30 so that input energy is applied between cathode and grid. The output energy may be taken from a coaxial line comprising shell 35 and a second conductor 38 which is capacitively coupled to anode 26 by means of an anode extension 39 and an extension 40 of conductor '38 overlapping therewith. The extensions 39 and '40 provide substantially a short circuit connection for alternating current energy but provide a blocking condenser for the direct current supply voltages for the tube. The anode grid output may be tuned to the desired impedance value by means of a tuning plunger 41 between inner surface of conductor 35 and conductor 38. This impedance provides the plate impedance Z .(Fig. 4).

Here again, it will be seen there is provided a coaxial amplifier of the grounded grid type which may be provided with coaxial input and output leads. 'In this instance thereexists within the tube unwanted capacitances which it is desired to neutralise designated as Cop, Ckg, and C (Fig. 4). In order to adjustably control or neutralise these capacities a tuning plungerisarranged as shown at 42 between the extension 32 and the inner surface of conductor .38. In order to preserve the desired blocking ."for the various direct currentsupply potentials tuning plunger 42 may be made .in two. parts.comprising a portion 43 in conductive connection 38 and a-portion 44 in conductive connection with lead 32, these portions being separated by an annular ring 4. (By adjustment .of the flange '42 .to the desired position the inductive reactance Lu (Fig 4) can be obtained.

Itwill-be again noted that with the neutralised amplifier a controlled feedback oscillator of 3 may be quite simply obtained using the tube having theauxiliary cathode extension whereas the neutralising or controlling circuit for an amplifier using the conventional .tube havinga cathode lead from only one endis much/more complex.

While I have illustrated my invention in connection with andapplied to particularcircuits it will be readily understood that the principles thereof are not limited .to the precise embodiments and circuitsasshown.

Many modifications and variations .of my invention willreadily .be apparent tothose skilled in the art.

While I have described .above the principles of my invention,inconnection'with specific apparatus, it is to be clearly understood that this description. is made only by way:of example'and not asa limitation tothe scopeof my invention as set forth in the objects thereof and in the accompanying claims.

What I claim: is:

1. An amplifier of the coaxial line type-comprising .an electron discharge device having an indirectly heated :cathode, anodeand grid electrode coaxially mounted, .a resonator comprising an outer shell coupled to the anodeaeleotroderfor alternatingcurrent transfer, a. first hollow cathode lead concentric with said outer shell extending into said devicefrom' one end, heater leads within. said hollow lead, a second cathode lead extending out froinsaid device from the other end and concentric with .saidouter shell, conductor means within said shell and concentric with said second cathode lead, means for coupling said conductor means with said grid electrode, adjustable plunger tuning means between said outer shell and said conductor means and between said conductor means and said second cathode lead, said plunger means between said conductor means and. said second cathode lead being positioned to provide a neutralizing inductance of the desired degree for the grid-cathode capacitance of said electron discharge device, and a tuning plunger between said outer shell and said first cathode lead to provide an output resonator.

2. An amplifier according to claim 1, further comprising alternating energy input means coupled between said outer shell and said conductor means, and alternating energy output means coupled to said output resonator.

ERVIN M. BRADBURD.

References Cited in the file of this patent UNITED STATES PATENTS 

